1. Field of the Invention
The present invention relates to a medical instrument used to implant seeds, such as radioactive seeds, into a patient""s body. In particular, the present invention relates to a drive mechanism for a medical instrument.
2. Description of the Related Art
For treating prostate cancer, radioactive seeds are provided to various locations within a patient""s prostate gland, by way of a medical instrument, also called a seed implantation device. Typically, a base unit which includes an ultrasound unit is used to determine the exact location of the patient""s prostate gland with respect to the base unit. The base unit is capable of being moved either towards the patient or away from the patient.
The ultrasound unit includes a probe, which is inserted into the patient""s rectum while the patient is lying on his back. A grid template is mounted onto the base unit, whereby the grid template includes a plurality of rows and columns of needle holes in which a needle can be inserted. Typically, the grid template includes a 13 by 13 matrix of needle holes, whereby adjacent holes on a row or a column are spaced 5 mm apart. Every other row is labeled with a number (e.g., 1, 2, etc.) on the grid template, and every other column is labeled with an alphabetic character (e.g., A, B, etc.). There is a direct relation between the centerline axis of the ultrasound probe and the position of the holes of the grid template.
Based on information obtained from the ultrasound unit, a needle is positioned through a particular hole (e.g., B5 hole) on the grid template, and then the needle is inserted into a region within the patient""s body in which the prostate gland is located. By using the ultrasound unit, a precise position of the proximal and distal positions (relative to the ultrasound unit) of the prostate gland can be determined and recorded. The distal position (relative to the ultrasound unit) of the prostate gland is also called the xe2x80x9czero retraction pointxe2x80x9d. Once the prostate gland position information is obtained, a seed implantation plan can be determined by a doctor, where the plan corresponds to a sequential process for injecting seeds into particular locations within the patient""s prostate gland. Such treatment is generally started by placing the end of the needle (e.g., bevel end of a bevel needle or the end of a trocar needle) at the zero retraction point, and then start applying seeds with respect to that reference point.
For a conventional seed implantation device, a needle is first placed into a particular needle hole of a grid template, and then the seed implantation device is held in place by a doctor and attached to the needle. The seed implantation device is then used to inject one or more seeds into the patient""s body through the needle. When finished with that hole, the seed implantation device is detached from the needle, and placed aside. Then, the needle is removed from the grid template, and a new needle is positioned at another needle hole of the grid template, according to the specific plan for treating the patient""s prostate gland. Alternatively, some physicians prefer to insert an entire row of needles onto the grid template, and thereby move from needle to needle. Other physicians implant all needles required at the deepest depth position, and then continue with all needles required at the next-deepest depth position, and so forth. One conventional seed implantation device is called a MICK applicator, and requires the operator to physically reposition the MICK applicator back onto a new needle positioned onto the grid template. Such an applicator is described in U.S. Pat. No. 5,860,909, entitled Seed Applicator for Use in Radiation Therapy.
The MICK applicator is manually moved by the operator between seed implant locations. This results in inaccuracies due to the operator not being capable of precisely retracting the medical instrument to a next seed implant position, due to human error and the size and weight of the medical instrument.
The present invention includes a drive mechanism for a medical instrument, that provides for precise indexing of the medical instrument between seed implant locations.
The present invention also includes a stylet carriage assembly within a medical instrument, which includes a stylet for pushing a seed from a seed cartridge shuttle all the way to a distal end of a needle cannula that is coupled to the medical instrument.
The present invention also includes a drive mechanism for a medical instrument, which provides for needle spin movement at precise times during movement of the medical instrument between seed implant positions.
Needle spin allows trapped air to be vented, preventing vacuum or pressurization of the air. In addition, friction between the seeds and the needle are reduced by relative dynamic motion.
In one configuration, a medical instrument includes a drive assembly that provides for drive movement of the medical instrument. When a handle on the medical instrument is moved from a first home position to a second position, the drive assembly causes a carriage assembly within the medical instrument to move in a distal direction, so as to cause a stylet coupled to the carriage assembly to move in the distal direction. The stylet is in line with a seed provided within an extended shuttle of a seed cartridge also located within the medical instrument, and the stylet pushes the seed all the way to a distal end of a needle cannula that is coupled to a distal end of the medical instrument. That way, the seed is in position to be deposited within a patient.
When the handle is moved from the second position to a third, fully engaged position, the medical instrument is caused to index or move a precise amount, by way of the drive assembly. During the index movement of the medical instrument, the stylet is maintained at its fully-extended, most-distal, position. Also, during the index movement of the medical instrument, the drive assembly controls spin movement of the needle cannula, so that the needle cannula spins as it moves between seed implant positions.
As the handle is retracted from the third position to the second position, the needle cannula spins in an opposite direction, while the medical instrument remains in place (does not index). As the handle is further retracted from the second position to the first position, the stylet moves back to its most-proximal position within the medical instrument, to thereby be positioned for a next seed to be implanted at the next seed implant location within the patient.
The drive mechanism is configured to provide an assortment of internal movements within the medical instrument, such as drive carriage movement and index movement of the entire medical instrument, based on small movements of the handle.
According to one aspect of the present invention, a drive mechanism for a medical instrument includes at least one gear that causes index movement of the medical instrument in accordance with operator-actuation of a trigger on the medical instrument.
According to another aspect of the present invention, a medical instrument includes a coupling portion for coupling to a needle cannula. The medical instrument also includes a stylet that is provided within a housing of the medical instrument and that is configured to move from a rest position in which the stylet is spaced apart from the needle cannula, to an engaged position in which the stylet moves within the needle cannula, to thereby propel a seed obtained from a cartridge within the medical instrument into a distal end of the needle cannula.
According to yet another aspect of the present invention, a method for implanting at least one seed into a patient includes actuating a trigger of a medical instrument from a first position to a second position, to thereby cause a seed to be placed at a distal end of a needle coupled to the medical instrument. As a result of the actuating step, moving a stylet within the medical instrument from a first position to a second position, whereby the stylet is moved from a proximal position within the medical instrument to a distal position within the medical instrument, and whereby the stylet pushes a seed to the distal end of the needle coupled to the medical instrument as a result.